CODEWITHSUNDEEP
c#.netwpfxaml
Alexander Ventura
Alexander Ventura

Reputation: 1160

Restricting Input in WPF

I am creating a custom control that when invoked in the XAML can be set to only allow certain types of inputs:

<lib:CustomControl RestrictTo="UnsignedIntegersOnly" ... ></CustomControl>

Where the UnsignedIntegersOnly is part of an Enum containing the set of allowed restrictions.

If the user inputs something that is not allowed, the control will throw a validation error and not allow him to continue to the next form/page/etc.

My vision for implementing this, was to, in the underlying TextBox that makes up this control, bind its text field to a validation rule which will be passed as an input the RestrictTo value that was specified in the CustomControl XAML declaration. Then in that ValidationRule class, handle the RestrictTo specific validation and return whether the validation was successful or not.

This is where I am not quite sure how to proceed. Is it even possible to pass arguments to the ValidationRule in such a seemingly dynamic manner? I am setting a property, RestrictTo, of my control and then passing that to its validation.

If it is possible, how would it be done? What sort of binding or resource linking should I use?

Upvotes: 1

Views: 1616

Answers (2)

Wallstreet Programmer
Wallstreet Programmer

Reputation: 9677

Below code should get you started. It is a user control and not a custom control. I recomend you get your code working as a user control first and then convert it to a custom control. Bind Valid property to some property in your viewmodel that controls user workflow.

XAML:

<UserControl x:Class="WpfApplication.ValidatingControl"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
             mc:Ignorable="d" >
    <StackPanel Orientation="Horizontal">
        <TextBox Name="_textBox" TextChanged="OnTextChanged" Background="LightGray" Width="200"/>
        <TextBlock Name="_messageText" Foreground="Red" />
    </StackPanel>
</UserControl>

Code behind:

using System.Windows;
using System.Windows.Controls;

namespace WpfApplication
{
    public partial class ValidatingControl : UserControl
    {
        public ValidatingControl()
        {
            InitializeComponent();
        }

        public enum Restrictions
        {
            UnsignedIntegersOnly,
            SmallIntegersOnly        
        }

        public static readonly DependencyProperty RestrictToProperty =
            DependencyProperty.Register("RestrictTo", typeof(Restrictions), typeof(ValidatingControl), new PropertyMetadata(Restrictions.UnsignedIntegersOnly));

        public Restrictions RestrictTo
        {
            get { return (Restrictions)GetValue(RestrictToProperty); }
            set { SetValue(RestrictToProperty, value); }
        }

        public bool Valid
        {
            get { return (bool)GetValue(ValidProperty); }
            set { SetValue(ValidProperty, value); }
        }

        public static readonly DependencyProperty ValidProperty =
            DependencyProperty.Register("Valid", typeof(bool), typeof(ValidatingControl), new UIPropertyMetadata(false));

        private void OnTextChanged(object sender, TextChangedEventArgs e)
        {
            ValidateText(RestrictTo, _textBox.Text);
        }

        private void ValidateText(Restrictions restrictTo, string text)
        {
            // validate text, update _messageText, update Valid 
        }
    }
}

Upvotes: 0

aybe
aybe

Reputation: 16662

You might be interested in using a MaskedTextBox control, it will restrict what the user can input in the TextBox.

As there's no official control from Microsoft for WPF I would suggest the following from Xceed :

MaskedTextBox (it's free to use :-)

Here you have the syntax of the mask :

http://msdn.microsoft.com/en-us/library/system.windows.forms.maskedtextbox.mask.aspx

<Window x:Class="WpfApplication1.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:xctk="http://schemas.xceed.com/wpf/xaml/toolkit"
        Title="MainWindow" Height="350" Width="525">
    <Grid>
        <xctk:MaskedTextBox Mask="0000"></xctk:MaskedTextBox>
    </Grid>
</Window>

If you have Visual Studio 2012 you can easily get this package through NuGet :

(right-click on your project )

enter image description here

Note : on my answer to your previous question, I extensively used validation rules in the link I posted but I'd say that if there are some times where you can avoid it through the means of a well-crafted component/control, then it's wise to do so. As @Barn pointed out on your previous question, a generic validation rule might be a hard thing to do and somewhat questionable as you'll have to handle all the types in it, IMO it's a little counter-intuitive as validators and converters are generally specific against being generalist; you're likely to waste more time on it than it's worth and it will be probably less re-usable than you think it could be. (source : my experience)

Upvotes: 1

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